MECHANISM FOR VISCOELASTIC POLYMER SOLUTION PERCOLATING THROUGH POROUS MEDIA

The pore throat of porous media is modeled as a constricted channel or expanded channel. The flow of viscoelastic polymer solution in pore throat model is studied by numerical method. Relationship between pressure drop and flow rate is developed,viscoelasticity and throat size are found to be two main factors in high flow resistance. According to pore throat model,2-D stochastic channel bundle is put forward to model porous media,which is composed of pore throat models in series -parallel connection with size and length accord to Haring -Greenkorn stochastic distribution. Percolation model of viscoelastic fluid is developed on the basis of Darcy equation and pressure drop vs. flow rate relation in 2-D stochastic channel bundle. Results indicate that the seepage ability of viscoelastic polymer solution decreases with the increase of viscoelasticity,injection rate,and heterogeneity as well as the decrease of mean pore size of porous media. The high pressure drop of viscoelastic fluid at the connection of pore to throat plays a great role in its anomalous high flow resistance through porous media.     

INFLUENCE OF SURFACTANT ON TWO-PHASE FLOW REGIME AND PRESSURE DROP IN UPWARD INCLINED PIPES

The influence of a surfactant on the two-phase flow regime and the pressure drop in upward inclined pipes is investigated for various gas/liquid flow rates.The air/water and air/100 ppm sodium dodecyl sulphate aqueous solution are used as the working fluids.The influence of the surfactant on the two-phase flow regime in upward inclined pipes is investigated using the electrical tomographic technique.For 0o,2.5o and 5o pipe inclinations,the surfactant has obvious effect on the transition from the stratified wavy flow to the annular flow,and the range of the stratified smooth flow regime is also extended to higher gas velocities.For 10o pipe inclination,no stratified flow regime is observed in the air/water flow.In the air/surfactant solution system,however,the stratified flow regime can be found in the range of and.For all inclination angles,the changes of the pressure gradient characteristics are accompanied with the flow pattern transitions.Adding surfactant in a two-phase flow would reduce the pressure gradient significantly in the slug flow and annular flow regimes.In the annular flow regime,the pressure gradient gradually becomes free of the influence of the upward inclined angle,and is only dependent on the property of the two-phase flow.     

SIMULATION OF THE TWO PHASE FLOW OF DROPLET IMPINGEMENT ON LIQUID FILM BY THE LATTICE BOLTZMANN METHOD

A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suitable for solution of twophase flow problem at high density and viscosity ratios of liquid to vapor and phase transition between liquid and its vapor.The roles of the vapor flow,the density ratio of liquid to vapor and the surface tension of the droplet in the splashing formation are discussed.It is concluded that the vapour flow induced by the droplet fall and splash in the whole impinging process may affect remarkably the splash behaviour.For the case of large density ratio of liquid to vapor a crown may engender after the droplet collides with the film.However,for the case of small density ratio of liquid to vapor a "bell" like splash may be observed.     

LIQUID PHASE FLOW ESTIMATION IN GAS-LIQUID TWO-PHASE FLOW USING INVERSE ANALYSIS AND PARTICLE TRACKING VELOCIMETRY

An inverse analysis algorithm is proposed for estimating liquid phase flow field from measurement data of bubble motion. This kind of technology will be applied in future for various estimation of fluid flow in rivers, lakes, sea surface flow, and also microscopic channel flow as the problem-handling in civil, mechanical, electronic, and chemical engineering. The relationship between the dispersion motion and the carrier phase flow is governed and expressed by the translational motion equation of spherical dispersion. The equation consists of all the force components including inertia, added inertia, drag, lift, pressure gradient force and gravity force.Using this equation enables us to estimate the carrier phase flow structure using only the data of the dispersion motion.Whole field liquid flow structure is also estimated using spatial or temporal interpolation method. In order to verify this principle, the Taylor-Green vortex flow, and the Karman vortex shedding from a square cylinder have been chosen. The results show that the combination of the inverse analysis and Particle Tracking Velocimetry (PTV) with the spatio-temporal postprocessing algorithm could reconstruct well the carrier phase flow of the gas-liquid two-phase flow.     

A PHYSICAL MODEL FOR PREDICTING THE PRESSURE DROP OF GAS-LIQUID SLUG FLOW IN HORIZONTAL PIPES

A comprehensive treatment of all sources of pressure drop within intermittent gas-liquid flow is presented. A slug unit is divided into three parts and the pressure gradient of each part is calculated separately. In the mixing zone the momentum theory is employed and the mixing process between the film and slug is simulated by a two-dimensional wall jet entering a large reservoir to calculate the mixing length. The boundary layer theory is utilized to calculate the pressure drop for the slug body and the momentum equation of the film zone is integrated to calculate the pressure drop for the film zone. The pressure drop predicted in present model is in good agreement with all the measurements.     

LIQUID-GAS TWO PHASE FLOW RATES METERING BY DUAL PRESSURE DIFFERENTIAL MEASUREMENTS

The measurement of the overall mass flow rates in a two phase, gas/liquid pipeline is considered on the basis of dual pressure differential measurements for a combined contraction/frictional pipe type of flow meter and a numerical model to predict overall mass flow rates from pressure differentials measured from this type of flow meter is presented. The experiments generally conform with the predictions of the flow rates prediction model. Whilst the practicability of such metering of two phase flows is clearly demonstrated, application of the method would require careful calibration to allow for the influence of nozzle coefficients, pipe Reynolds number and void fraction upon the one dimensional compressible flow equations through wall friction factor and interphase slip effects.     

3-D NUMERICAL SIMULATIONS OF FLOW LOSS IN HELICAL CHANNEL

The flow loss of a helical channel Magnetohydrodynamic(MHD) thruster without MHD effect was numerically studied with 3-D simulations,and a flow loss coefficient was defined to quantify the flow loss and its influencing factors were studied.The results show that decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number,and it declines slowly when and,a flow guide makes the flow more smooth and uniform,especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly,by about 30% with the averaged value of from 0.0385 to 0.027,a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions,thus reduces the rotational kinetic pressure with the averaged value of declining about 4% from 0.0385 to 0.037,and decreases with a rectifier’s axial length when.     

Numerical prediction of 3-D periodic flow unsteadiness in a centrifugal pump under part-load condition

Numerical simulation and 3-D periodic flow unsteadiness analysis for a centrifugal pump with volute are carried out in whole flow passage, including the impeller with twisted blades, the volute and the side chamber channels under a part-load condition. The pressure fluctuation intensity coefficient （PFIC） based on the standard deviation method, the time-averaged velocity unsteadiness intensity coefficient （VUIC） and the time-averaged turbulence intensity coefficient （TIC） are defined by averaging the results at each grid node for an entire impeller revolution period. Therefore, the strength distributions of the periodic flow unsteadiness based on the unsteady Reynolds-averaged Navier-Stokes （URANS） equations can be analyzed directly and in detail. It is shown that under the 0.6Qd~. condition, the pressure fluctuation intensity is larger near the blade pressure side than near the suction side, and a high fluctuation intensity can be observed at the beginning section of the spiral of the volute. The flow velocity unsteadiness intensity is larger near the blade suction side than near the pressure side. A strong turbulence intensity can be found near the blade suction side, the impeller shroud side as well as in the side chamber. The leakage flow has a significant effect on the inflow of the impeller, and can increase both the flow velocity unsteadiness intensity and the turbulence intensity near the wall. The accumulative flow unstea- diness results of an impeller revolution can be an important aspect to be considered in the centrifugal pump optimum design for obtaining a more stable inner flow of the pump and reducing the flow-induced vibration and noise in certain components.     

A NOVEL DESIGN OF COMPOSITE WATER TURBINE USING CFD

This paper presents computational investigation of a novel design of composite material axial water turbine using Computational Fluid Dynamics(CFD).Based on three-dimensional numerical flow analysis,the flow characteristics through the water turbine with nozzle,wheel and diffuser are predicted.The extract power and torque of a composite water turbine at different rotating speeds were calculated and analyzed for a specific flow speed.The simulation results show that using nozzle and diffuser can increase the pressure drop across the turbine and extract more power from available water energy.These results provide a fundamental understanding of the composite water turbine,and this design and analysis method is used in the design process.     

虹吸管气液两相流压降特性试验

通过系列试验量测了不同安装高度、不同水位差时虹吸管水平管段的压降、含气率及过流量,探讨和分析了虹吸管气液两相流压降的变化规律及气液两相流流型不同时影响管道压降的因素。结果表明,气液两相流管道压降与液相满流时压降规律相同,即压降值随管道水头的增大而增大;但是,与液相有压管流不同,水位差一定时压降值随安装高度的增大而减小。当虹吸管内为气泡流时,气泡存在对沿程阻力系数λ影响很小,可忽略不计。管道实测压降小于计算值的原因是气液两相压降减小率等于流速减小率。当虹吸管内为过渡流和气团流时,气液两相压降减小率与流速减小率相差较大,实测压降的减小不仅与流速减小有关,含气率的大小对气液两相压降的影响也不可忽略,含气率的增大使气液两相流动阻力增大,即压降增大。     

虹吸管道水气两相流动过流能力的试验分析

通过对虹吸式输水管道输水能力的试验研究,观测到不同安装高度下的气液两相流现象。量测了不同安装高度相应水位差下的流量的大小,并分析了流量变化规律。研究发现,随着安装高度的增大,虹吸管内气液两相流流型由气泡流转化为气团流。分析原因发现在安装高度h_s=2 m时,流量减小率与面积减小率相等,表明气液两相流时过流面积小于液相满流时过流面积是流量的减小的主要原因;当安装高度h_s2 m时,流量减小率与面积减小率相差较大,表明流量的减小不仅与面积变化有关,还应与沿程阻力系数有关。掺气浓度的增大使管内压降增大,压降的增大导致了管内阻力增大,从而使沿程阻力系数增大,而导致流量减小。     

UNSTEADY FLOW ANALYSIS AND EXPERIMENTAL INVESTIGATION OF AXIAL-FLOW PUMP

The three-dimensional unsteady turbulent flow in axial-flow pumps was simulated based on Navier-Stoke solver embedded with k-ε RNG turbulence model and SIMPLEC algorithm.Numerical results show that the unsteady prediction results are more accurate than the steady results,and the maximal error of unsteady prediction is only 4.54%.The time-domain spectrums show that the static pressure fluctuation curves at the inlet and outlet of the rotor and the outlet of the stator are periodic,and all have four peaks and four valleys.The pressure fluctuation amplitude increases from the hub to the tip at the inlet and outlet of the rotor,but decreases at the outlet of the stator.The pressure fluctuation amplitude is the greatest at the inlet of the rotor,and the average amplitude decreases sharply from the inlet to the outlet.The frequency spectrums obtained by Fast Fourier Transform(FFT) show that the dominant frequency is approximately equal to the blade passing frequency.The static pressure on the pressure side of hydrofoil on different stream surfaces remains almost consistent,and increases gradually from the blade inlet to the exit on the suction side at different time steps.The axial velocity distribution is periodic and is affected by the stator blade number at the rotor exit.The experimental results show that the flow is almost axial and the pre-rotation is very small at the rotor inlet under the conditions of 0.8 QN -1.2 QN.Due to the clearance leakage,the pressure,circulation and meridional velocity at the rotor outlet all decrease near the hub leakage and tip clearance regions.     

混凝土大坝坝体渗漏探测技术及其应用

为研究混凝土坝体渗漏探测技术,以某水利枢纽工程混凝土重力坝裂隙式渗漏为研究对象,采用伪随机流场法探测渗漏入水口;采用钻孔及钻孔测试技术(温度测井、声波测井、钻孔电视观察、压水试验等)定位渗漏通道。研究结果表明:①当坝外有明显渗漏出水口时,伪随机流场法可以精确圈定坝内渗漏入水口;②坝体裂隙一般垂直坝体方向分布(如连接横缝)或沿坝体方向分布(如水平缝),或者两者皆有且连通;③坝顶钻孔及钻孔测试方法能够查明渗漏通道的高程及桩号分布范围。针对混凝土坝体裂隙式渗漏,采用伪随机流场法和钻孔测试技术综合探测,具有准确、快速、便捷、安全的特点,对于其他类似工程问题有一定借鉴意义。     

三峡模型水轮机转轮的流态观测及过流通道内水压脉动试验研究

针对三峡机组运行水头变幅大、机组钤芳最成工况运行时间长等特点，在开发的三峡模型乐轮机组上进行了流态观测与水压脉动试验，本次试验选取了三峡电站动物范围内不同水头、不同负荷下的５５个工况，对该选定工况进行如下工作，即利用光导内窥交易和闪光测频仪对模型转轮叶片进出口流态进行了不同空化系数下的观测及描绘；对过流通道上布置的８个水压脉动测点，进行了电站装置空化系数下的水压脉动试验；以及在同一工况的不同空化系     

竖向进水管布置对ABR液相流态影响的PIV试验研究

在折流式厌氧反应器(Anaerobic Baffled Reactor,ABR)不同进水管悬空高度和不同进水流量组合的工况下,利用激光粒子图像测速技术(particle image velocimetry,PIV)对ABR的第一格室液相流态进行了研究,测得反应器内降流区和升流区关键截面的流场数据,获得了液相速度和涡量强度与悬空高度的关系曲线;同时研究了相关流场特征,包括流线图谱和涡量场。结果表明:对于ABR的第一格室,合理的进水管悬空高度可以保证良好的进水流态,促使ABR涡量面积分布均匀,有效防止局部沟流和液相死区,确保ABR高效稳定运行。根据试验分析结果,提出了设计时可供参考的进水管悬空高度的取值范围:流量在0.018～0.270 m³/h时,悬空高度的取值范围为230～530 mm;流量在0.558～0.846 m³/h时,悬空高度的取值为530 mm。     

Biofilm growth and hydrodynamic behaviour in the biological plate tower (BPT) with and without hanging biomass (BPT-HB)

Deodorization and volatile organic compound abatement from polluted air streams can be accomplished with the biological plate tower (BPT), which has proved to be a reliable alternative to biofilters and biotrickling filters. Unlike those, the BPT is a non-clogging device, with constant active surface, and steady performance, making it ideal for scale-up and modelling. The initial BPT design needed improvement for better performance. The cylindrical body (circular plates) was replaced by a rectangular cuboid (rectangular plates). Holes in the plates did augment the amount of active biomass (hanging from the holes and under the plates), without reducing the transfer of toluene from the gaseous to the liquid phase. The diminished distance between plates was well tolerated in co-current flow, allowing much higher quantities of biomass in the same reactor volume. With 18 and 14 mm spacing between adjacent plates, the BPT, with and without holes, was tested for flooding, holdup and pressure drop. Several gas and liquid flows were tested, both in co-current and counter-current. In hydrodynamic terms, the BPT-HB with co-current flow was clearly the best option. Higher stability with higher flow rates, and lower pressure drops were observed. The inoculum was obtained from wastewater plant activated sludge (petrochemical industry).     

PARAMETRIC STUDY ON THE THRUST OF BUBBLY WATER RAMJET WITH A CONVERGING-DIVERGING NOZZLE

To predict the thrust of bubbly water ramjet with a converging-diverging nozzle, the physical processes occurring in the diffuser, mixing chamber and nozzle were analyzed. The mathematical models were constructed separately under the restrictions of certain assumptions. The bubbly nozzle flow was examined using a two-fluid model and accomplished by specifying the water velocity distribution in the nozzle. The numerical analysis of flow field in the nozzle shows that the Mach number at the throat is 1.009, near unity, and supersonic bubble flow appears behind the throat. There is greater thrust produced by bubbly water ramjet, compared with single-phase air ramjets. Subsequently, the influences of vessel velocity, air mass flow rate, inlet area A_m, area ratio (i.e., mixing chamber to inlet area A_m/A_i), and initial bubble radius on the thrust were emphatically investigated. Results indicate that the thrust increases with the increase of air mass flow rate, inlet area and the area ratio, and the decrease of initial bubble radius. However, the thrust weakly depends on the vessel velocity. These analytical and numerical results are useful for further investigation of bubbly water ramjet engine.     

THREE-DIMENSIONAL NUMERICAL MODELING OF SECONDARY FLOWS IN A WIDE CURVED CHANNEL

Most natural rivers are curved channels, where the turbulent flows have a complex helical pattern, as has been extensively studied both numerically and experimentally. The helical flow structure in curved channels has an important bearing on sediment transport, riverbed evolution, and pollutant transport study. In this article, different turbulence closure schemes i.e., the mixing-length model and the k – ? model with different pressure solution techniques i. e., hydrostatic assumptions and dynamic pressure treatments are applied to study the helical secondary flows in an experiment curved channel. The agreements of vertically-averaged velocities between the simulated results obtained by using different turbulence models with different pressure solution techniques and the measured data are satisfactory. Their discrepancies with respect to surface elevations, superelevations and secondary flow patterns are discussed.